Field
The presently disclosed subject matter relates to a semiconductor light-emitting device having a plurality of light-emitting elements such as light-emitting diode (LED) elements arranged in a matrix.
Description of the Related Art
A prior art semiconductor light-emitting device formed by LED elements arranged in a matrix including rows and columns has been used as a vehicle headlamp. In such a semiconductor light-emitting device, luminous intensities of the LED elements are individually controlled in real time to realize an adaptive drive beam (ADB) and an adaptive front-lighting system (AFS) (see: JP2013-54849A & JP2013-54956A).
In an ADB control, when a preceding vehicle including an on-coming vehicle is detected by a radar unit or the like, the luminous intensities of only the LED elements against the preceding vehicle are decreased to decrease the illuminance against the preceding vehicle while a high-beam mode is maintained. As a result, glaring against the preceding vehicle can be suppressed while the visibility in a high-beam mode can be maintained except for the preceding vehicle.
In an AFS control, when a steering angle read from a steering angle sensor or the like is larger than a predetermined value, the LED elements having high luminous intensities are shifted from a central area of the device to a right side or a left side of the device, to substantially decline the optical axis of the device while the visibility in a high-beam mode is maintained.
FIG. 1A is a plan view illustrating the above-mentioned prior art semiconductor light-emitting device, and FIG. 1B is a cross-sectional view taken along the line B-B in FIG. 1A. As illustrated in FIGS. 1A and 1B, the semiconductor light-emitting device includes a semiconductor wafer (body) 1 in which blue LED elements D11, D12, . . . , D33 in three rows, three columns are formed and a phosphor layer P1 including yitrium aluminium garnet (YAG) particles P10 for wavelength-converting blue light into yellow light to form white light is formed on the LED elements D11, D12, . . . , D33, and a support body 2 for supporting the semiconductor body 1. In this case, the semiconductor body 1 is wafer-bonded onto the support body 2. In FIG. 1B, each of the LED elements D11, D12, . . . , D33 are mesa-shaped, so that the distance between side faces of two adjacent LED elements is gradually decreased toward the support body 2.
Note that each of the LED elements D11, D12, . . . , D33 is square or rectangular viewed from the top, so that the LED elements D11, D12, . . . , D33 can be in close proximity to each other.
In the semiconductor light-emitting device of FIGS. 1A and 1B, since there are still relatively large spaces between the LED elements D11, D12, . . . , D33, even when the LED elements D11, D12, . . . , D33 are operated to emit lights L11, L12, . . . , L33, respectively, as illustrated in FIG. 2A, dark regions DR would be created at the spaces. As a result, as illustrated in FIG. 2B, light emitting regions ER22 and ER23 of the LED elements D22 and D23 would be decreased. In this case, the larger the spacing between the LED elements D11, D12, . . . , D33, the larger the dark regions DR.
On the other hand, when the LED elements D11, D12, . . . , D33 are closer to each other as illustrated in FIGS. 3A and 3B, the dark regions DR would be reduced in size to increase the light emitting regions. In this case, however, when the LED elements D11, D12, D13, D21, D23, D31, D32, D33 except for the LED element D22 are operated to emit lights L11, L12, L13, L21, L23, L31, L32, L33, leakage lights LL would be leaked into the non-operated LED element D22 from its adjacent operated LED elements. Therefore, weak light would be emitted from the non-operated LED element D22, so that optical crosstalk would be generated between the non-operated LED element and its adjacent operated LED elements.
Thus, in the semiconductor light-emitting device of FIGS. 1A and 1B, it is preferable that both of the dark regions DR and the optical crosstalk be as small as possible; however, there is a trade-off relationship between the dark regions DR and the optical crosstalk.